The present disclosure is related to downhole drilling and, more particularly, to automating downhole drilling based on the profile and energy of the wellbore being drilled.
The quality of a wellbore or borehole is generally related to the “smoothness” of the wellbore. Various trajectory models for drilling a wellbore have been proposed, with varying degrees of resulting wellbore smoothness. The simplest model, the tangential model, consists of straight line sections. Thus, the slope of this model is discontinuous at survey points along the length of the wellbore. Another common model is the minimum curvature model, which consists of circular arcs. This model has continuous slope, but discontinuous curvature. By far the most common method for trajectory modeling and drillstring analysis is the “torque-drag” model which calculates additional load during tripping in and tripping out operations where torque is due to rotation of the drillstring and drag is the excess load compared to rotating drillstring weight due to friction generated by drillstring contact with the wellbore.
The smoothness of the wellbore may be manifested in a number of ways, all adversely affecting the efficiency of the drilling process and increasing drilling and well completion costs. Presently, different parameters such as wellbore tortuosity, curvature, torsion, and various drilling indices are either used to quantify the wellbore path or estimate the difficulty of drilling a smooth wellbore. Furthermore, there is no clear criterion for defining the quality of the wellbore. For instance, drilling indices that are taken into account generally describe the quality of the borehole more subjectively rather than qualitatively quantifying the borehole. In some cases drilling indices are used purely as a measure of how difficult the well will be to drill, and not how smoothly it could be drilled.
Today, autonomous computer-controlled drilling operations (i.e., “drilling automation”) are approaching reality because it promises to save rig time and deliver financial benefits to the well operator by automatically implementing a wellbore trajectory model. When the actual wellbore trajectory deviates from the planned wellbore path, it is imperative for a system to take corrective actions. For example, proportional-integral-derivative (PID) control used in wells today can provide negative feedback to the rotary steering drilling tools so as to bring the deviated drilling path back to the planned track. However, overshoots and undulations are quite often observed in PID control.